How can you calculate a medication dose for a rat? - briefly
Measure the rat’s weight in kilograms and multiply by the desired milligrams‑per‑kilogram dose. When converting a human dosage, apply allometric scaling (Rat Km = 6, Human Km = 37) using the formula Dose_rat = Dose_human × (Km_human / Km_rat) × (Weight_rat / Weight_human).
How can you calculate a medication dose for a rat? - in detail
To determine an appropriate drug amount for a laboratory rat, start with a dose expressed per unit body weight. The fundamental equation is:
[ \text{Required mass (mg)} = \text{Dose (mg·kg}^{-1}) \times \text{Animal weight (kg)} ]
Step‑by‑step procedure
- Obtain the species‑specific dose. Reference peer‑reviewed literature or product information for the drug’s recommended mg·kg‑¹ dose in rats.
- Measure the animal’s weight. Use a calibrated balance; record weight in grams and convert to kilograms (1 g = 0.001 kg).
- Calculate the absolute dose. Multiply the dose from step 1 by the weight from step 2. The result is the exact milligram amount needed for that individual.
- Convert to administration volume (if the drug is a solution).
[ \text{Volume (mL)} = \frac{\text{Required mass (mg)}}{\text{Solution concentration (mg·mL}^{-1})} ]
Adjust concentration so that the final volume does not exceed the maximum tolerated volume for the chosen route (e.g., ≤ 10 mL·kg‑¹ for oral gavage, ≤ 2 mL·kg‑¹ for intraperitoneal injection).
Allometric scaling when only a human dose is available
[ \text{Rat dose (mg·kg}^{-1}) = \text{Human dose (mg·kg}^{-1}) \times \frac{K_m\text{(human)}}{K_m\text{(rat)}} ]
Typical (K_m) values: human = 37, rat = 6. This conversion accounts for differences in metabolic rate and surface‑area–to‑mass ratios.
Illustrative calculation
- Target dose: 10 mg·kg‑¹ (rat‑specific).
- Rat weight: 250 g = 0.25 kg.
- Required drug mass: 10 mg·kg‑¹ × 0.25 kg = 2.5 mg.
- Solution concentration: 5 mg·mL‑¹.
- Administration volume: 2.5 mg ÷ 5 mg·mL‑¹ = 0.5 mL (within the 2 mL·kg‑¹ limit for i.p. injection).
Additional considerations
- Verify bioavailability for the selected route; adjust dose if oral absorption is incomplete.
- Maintain drug stability by preparing fresh solutions or using appropriate preservatives.
- Record each calculation, animal identifier, and administered volume in a laboratory notebook.
- Perform a double‑check of all numeric inputs before administration to prevent dosing errors.